Multi-functional antenna array apertures for military and commercial use promise a larger number of applications with better performance at lower overall cost, weight, and installation space. A central component in these systems is the ultra-wideband (UWB) phased antenna array. Traditional UWB arrays are very costly to build due to the high element density required for scanning across a wide range of frequencies. In order to make multi-functional apertures a viable option, there is significant interest in finding a way to reduce the cost of UWB array designs.
UWB arrays are commonly based on the flared-notch (Vivaldi) array element, e.g. as described in M. Kragalott. W. R. Pickles, and M. S. Kluskens, “Design of a 5:1 bandwidth stripline notch array from FDTD analysis,” IEEE Transactions on Antennas and Propagation, Vol. 48, pp. 1733-1741 (2000). The flared-notch is a popular element because it is relatively easy to manufacture and provides excellent bandwidth and scan performance. In recent years, UWB array research has focused on developing low-cost alternatives including: lower cost element designs, such as is described in W. Croswell, T. Durham, M. Jones, D. H. Schaubert, P. Frederich, and J. G. Maloney, “Wideband Array.” Modern Antenna Handbook, C. A. Balanis, Wiley (2008); manufacturing technologies, such as described in H. Holter, “Dual-Polarized Broadband Array Antenna With BOR-Elements, Mechanical Design and Measurements,” IEEE Trans. Antennas Propagat, vol. 55, pp. 305-312 (2007); and assembling techniques, such as described in M. W. Elsallal and D. H. Schaubert, “Electronically scanned arrays of dual-polarized, doubly-mirrored balanced antipodal Vivaldi antennas (DmBAVA) based on modular elements,” Conference Proceedings, IEEE Antennas and Propagation Society International Symposium, 9-14 Jul. 2006. These techniques are primarily intended to reduce the cost of UWB systems at the element level, but do not address the issue of excessive numbers of elements in large UWB systems.
Another approach described in B. Cantrell, J. Rao, G. Tavik, M. Dorsey, and V. Krichevsky, “Wideband Array Antenna Concept,” 2005 IEEE International Radar Conference Record, pp. 680-684, proposed a UWB array with reduced element count featuring a core of traditional wideband flared-notch elements surrounded by concentric rings of increasingly-larger (reduced bandwidth) elements, each new ring having the same number of radiators as the outer ring of the UWB core. This architecture was designed to achieve relatively-constant electrical aperture size versus frequency with significantly fewer elements than traditional UWB arrays. This concept is similar to thinned narrowband arrays, such as those described in R. Mailoux, Phased Array Antenna Handbook, 2nd ed.: Artech House (2005), because it leads to lower element count, but it also differs significantly in that (1) it is for UWB and not narrowband arrays, (2) the outer elements are scaled in size and (3) the aperture is not fully illuminated at all frequencies. The Cantrell concept was not practical for implementation due to the high number of different-size array elements as well as mutual coupling/structural integrity issues associated with element misalignment. It is therefore desirable to provide a UWB array of reduced size, complexity, and cost compared with previous such efforts.